Buy the Peak Racing 4200 mah lipo battery - no chassis modifications required, and the batteries are relatively inexpensive. I'd avoid brushless motors in the M-Chassis, since the final drive ratio wouldn't be very friendly with a higher-turn brushless motor (you'd have plenty of torque, but come up short on top speed). Lower turn (13.5 or less) would shred the drivetrain, provided you didn't shred the front tires first.
Drive the mini with the silver can motor first, upgrade the shocks, drive train and steering components, then start worrying about more power.
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